Adjustable probe

ABSTRACT

Touch-triggered probe comprising a fixed part, designed to be fastened onto a measuring machine or a machine tool, and a mobile contact feeler that can be oriented on two independent axes along a multiplicity of spatial directions.

REFERENCE DATA

This application claims priority from European patent application N^(o)EP03001836.0 filed on Jan. 29, 2003.

1. Field of the Invention

The present invention concerns a touch-triggered probe that can beoriented spatially along a multiplicity of directions. This probe isdesigned to be used more particularly, but not exclusively, in ahand-operated or automatic measuring machine or in a machine tool suchas for example a milling machine, for the three-dimensional measuring ofa piece that has been or is being machined.

2. Description of Related Art

Touch-triggered probes are measuring instruments used widely, though notexclusively, on production lines of mechanical pieces for accuratelychecking the dimensions or surfaces of the mechanical pieces.Touch-triggered probes are also used for three-dimensional measuring ofpieces of complex shape in order to reproduce or model them.

Generally, touch-triggered probes comprise a fixed part, designed to befastened onto a measuring machine or a machine tool, and a mobilefeeler, comprising a sphere at the end of an elongated rod and designedto be brought into contact with the piece to be measured.

In most applications, the touch-triggered probes are fastened on themobile arm of a machine whose spatial position is determinable preciselywith the aid of a hand-operated or automatic measuring system, such asfor example position encoders placed on the machine's axes. The mobilearm is displaced spatially to bring the probe's measuring feeler intocontact with the piece or surface to be measured. During contact, adeflective force is then applied onto the feeler, moving it out of itsinitial resting position. A sensor reacts to the feeler's slightestdisplacement, generating an electric signal that is sent either to theuser, in the form of a light signal, or to the machine's controlsoftware that thus determines, on the basis of the measuring system'sdata, the coordinates of the contact point in a given reference frame.For this purpose, electromechanical or optical sensors or movementsensors based on different principles, for example sensors comprisingconstraint gauges, are used in the prior art.

In the case of a three-dimensional touch-triggered probe, the linkbetween the feeler and the probe's fixed part is usually achieved alongthe principle of the Boys connection, such as for example through threecylindrical pins resting on six spheres so as to define six contactpoints between the fixed device and the feeler. Two-dimensional andone-dimensional probes are however also known.

When the probe is used for measuring pieces of complex shape withhollows and protuberances, it is difficult, if not impossible, to bringthe feeler into contact with the whole surface of the piece without theprobe's fixed part or the feeler's rod interfering with the elements ofthe piece to be measured. To remedy this inconvenience, probes are knownthat allow the contact feeler to be oriented in a plurality of spatialdirections. Generally, two independent rotation axes are required tocover all the possible orientations. A probe of this type is describedin European patent application EP-0'392'660-A2.

The rotation axes are preferably indexed, in the sense that they providea number sufficiently large but finite of predetermined and accuratelyreproducible resting positions. This disposition avoids the necessity ofagain calibrating the measuring machine after each change of thefeeler's orientation.

During measuring, the axes allowing the aforementioned prior art probeto be oriented are locked in one of the provided indexed positions. Whena different orientation of the probe is required, the user must manuallyunlock the axes, by acting on a wheel or on a lever provided to thiseffect, orient the probe as needed, and lock the axes again byrepositioning the wheel or lever in the initial locking position. Theseoperations can entail positioning errors, for example following aninvoluntary movement of the first axis during positioning of the secondaxis.

Another inconvenience of the probe described here above is that thelocking and unlocking operations require an external torque to beapplied onto the locking wheel, which is transmitted by the probe andits support to the mobile arm of the measuring machine. This net torquecauses mechanical efforts on the probe's support and can cause the wholeprobe to move. To avoid this inconvenience, the user must hold the probemotionless when acting on the locking wheel, which makes it difficult oreven impossible to perform this operation with a single hand.

BRIEF SUMMARY OF THE INVENTION

It is thus an aim of the present invention to propose a touch-triggeredprobe, capable of being oriented in a multiplicity of indexeddirections, whose positioning is performed reliably without risk ofpositioning errors.

It is another aim of the invention to propose a touch-triggered probethat does not have the limitations of the prior art.

According to the invention, these aims are achieved by the device thatis the object of the main claim, and notably by an adjustabletouch-triggered probe for orienting a measuring feeler relative to ameasuring apparatus, comprising:

a supporting element;

a first mobile element connected to said supporting element through afirst axis for turning said first mobile element relative to saidsupporting element;

a first resilient device for holding said first mobile element in alocked position, preventing said first mobile element from rotating;

a second mobile element connected to said first mobile element through asecond axis for turning said second mobile element relative to saidfirst mobile element;

a second resilient device, independent from said first resilient device,for holding said second mobile element in a locked position, preventingsaid second mobile element from rotating.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood by reading thedescription given by way of example and illustrated by the attachedfigures, in which:

FIG. 1 a shows a first embodiment of a touch-triggered probe accordingto the invention;

FIG. 1 b shows a fixed part of the touch-triggered probe according tothe invention represented in FIG. 1 a;

FIGS. 1 c and 1 d show the indexing mechanism of the first axis of thetouch-triggered probe according to the invention represented in FIG. 1a;

FIG. 1 e shows the demultiplying mechanism used for disengaging thefirst axis of the probe of FIG. 1 a;

FIGS. 2 a, 2 b and 2 c show in cross-section and elevation the indexingand demultiplying mechanisms of the second axis of the probe of FIG. 1a;

FIGS. 3 and 4, 5 a and 5 b show a second embodiment of the probeaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The first embodiment of the invention represented in FIGS. 1 a to 1 e isa touch-triggered probe 20 comprising a fixed part 250, represented indetail in FIG. 1 b, and designed to be fastened to the mobile arm of ameasuring machine through the threaded rod 251 or through any otherknown fastening means.

The fixed part 250 carries on its lower side 24 spheres 256, regularlydistributed along a circumference and partially protruding downwards.The spheres 256 define 24 indexed positions at a distance of 15 degreesfor the probe's first rotation axis, as will be explained further below.It is obvious that a different number of spheres can be used accordingto the desired number of indexed positions.

The mobile element 210, represented in FIGS. 1 c and 1 d, carries on itsupper side three cylindrical pins 217. The flat spring 215 presses themobile element 210 against the fixed element 250. In this situation,each of the pins 217 rests on two of the spheres 256, the six resultingcontact points determining the relative position of the elements 250 and210 in an accurate and reproducible fashion.

In view of the rotation symmetry of the fixed element, the mobileelement 210 can take up 24 indexed positions, at a distance of 15degrees from one another, around the first rotation axis 211corresponding to the probe's geometrical axis. The same result couldhave been obtained by other equivalent arrangements, for example byplacing the spheres on the mobile element and the pins on the fixedelement, or by replacing the spherical or cylindrical surfaces of thepins or of the spheres by inclined planes, or even by using sixcylindrical pins having each a single contact point with one of thespheres. It would also be possible to replace the flat spring 215 by anequivalent resilient device, for example a cylindrical spring or leafspring or by an element made of a resilient synthetic material.

The disengaging mechanism 300, represented in FIGS. 1 d and 1 e, allowsthe mobile element 210 to rotate around the axis 211. The transmission300 is constituted of a toothed wheel 301, driven by the four racks 305and by the inclined helical surfaces 302.

When two opposed buttons 310 are pressed, the racks 305 drive inrotation the toothed wheel 301 and the inclined planes 302 unitedtherewith and which, sliding on their bearings (not represented in thefigures), move the fixed element 250 away axially from the mobileelement 210. In the position where they are apart, the spheres 256protrude over the pins 217 without touching them, and rotation aroundthe axis 211 is possible.

The resting force of the pins 217 on the spheres 256 must besufficiently high to prevent any accidental movement of the mobile part210 during measuring. In this particular embodiment, the spring 215 isdimensioned for a total resting force of approximately 30 N, i.e. about10 N for each of the six contact points, since the pressure is exertedat 60 degrees relative to the axis.

It would be difficult to apply a force of 30 N directly on the buttons310. For this reason, the slope of the inclined surfaces 302 is chosento give a sufficient demultiplication ratio between the radial forceexerted on the buttons 310 and the axial force opposing the elasticityof the spring 215. A reduction ratio of 1:2 means an operation force onthe buttons 310 of about 15 N, i.e. approximately 1.5 Kgf, which theuser can exert without great difficulty. With this reduction ratio, therun of the buttons 310 remains contained within several millimeters.

The numerical values given here above must be interpreted as examplesparticularly suited to the presented embodiment. It would be possible tochose different values according to circumstances, for example accordingto the mass and the dimensions of the probe.

In order to ensure that the mobile element 210 is disengaged around therotation axis 211, it is necessary to act simultaneously on two opposedbuttons 310. In this manner, the external forces exerted on the probeare essentially in opposition to one another and perpendicular to therotation axis 211, the resulting force and torque are essentially niland any involuntary movement of the probe is prevented.

While the buttons 310 are pressed along the radial direction, the usercan make the mobile element 210 turn around the axis 211 by acting onthe same buttons in tangential direction. This operation is veryintuitive and can easily be performed with two fingers of a hand. Inthis condition, the distance between the spheres 256 and the pins 217 issufficient to avoid any contact or friction of the indexing surfaces,thus maintaining the positioning accuracy in indexed position. It isthus not necessary to release the buttons 310 to go from the unlockingto the rotation of the probe and then for locking the probe again.

The reduction ratio and the friction coefficients of the materials usedare chosen so that the transmission 300 is reversible, so that themobile element 210 returns spontaneously to an indexed position once thepressure on the buttons 310 is released, thus avoiding an accidental usein free position.

The first mobile element 210 is connected to a second mobile element 220capable of turning around a rotation axis 212, perpendicular to thefirst rotation axis 211, and to which a mobile feeler 30 of known typeis fastened, as can be seen in FIG. 2 a.

The second mobile element 220 is pressed against the first mobileelement 210 in the axial direction defined by the rotation axis 212 bythe compression spring 225. A crown of spheres 226 is provided on avertical side of the mobile element 220 and interacts with threecylindrical pins (not represented in the figure) placed on the adjacentside of the first mobile element 210 to define a predetermined number ofindexing positions that are exactly reproducible, in a manner similar tothat explained here above for the rotation of the first mobile element210.

In a possible variant embodiment, six cylindrical pins having each onlya single contact point can be used.

The disengaging and rotating system 400 of the second mobile element 220is represented in figure 2 b. The disengaging is performed by pressingon the two buttons 411 and 410. The axial force applied on the button410, capable of sliding axially around the piece 470, is transmitted bythe two levers 430 and 450 and by the horizontal arm 440, and ismultiplied and applied by the pin 461 and the rod 460 to the spring 225,in order to compress the latter, which suppresses the contact forcebetween 220 and 210. In this embodiment, the dimensions of the arms ofthe levers 430, 450 will be chosen of unequal length to obtain areduction ratio of the operation force of 1:2, as for the first mobileelement 210. A second spring 475, placed between the button 410 and thepiece 470, pushes axially towards the right in figure 2 a the secondmobile element 220 while allowing it to rotate.

When the button 410 is pressed, the second mobile element 220 isdisplaced towards the right of FIG. 2 a, so that the pins and theindexing spheres 226 no longer touch, and the second mobile element 220can turn around the axis 212. The rotation is impressed by the userthrough the button 410, which is united angularly with the piece 470through a pin, not visible in the figures.

The button 411, opposed to the button 410, has the double function ofgiving the finger a resting surface for exerting a force opposed to thatapplied on the button 410 and to facilitate the rotation of the element220 with two fingers. The button 411 is in fact united angularly withthe element 220 and is driven in rotation with the latter. Use of twoforces that are essentially opposed prevents efforts from beingtransmitted onto the probe's support and the whole probe from moving.

The action of the button 410 on the second mobile element 220 throughthe rod 460 is substantially aligned and opposed to the force exerted bythe spring 225, which ensures rectilinear movements without any jamming.

The electric signal generated by the feeler 30 is sent either to theuser, in the form of a light signal emitted by the light diode 50 (FIG.1 a), or to the machine's control software, which thus determines, onthe basis of the measuring system's data, the coordinates of the contactpoint in a given reference frame.

The lower part of the probe 20 has one or several protecting elements218 protruding out of the probe's body and whose function is to protectthe indexing mechanism from shocks against the measuring piece oragainst the supporting table. The protecting element 218 can be anenlargement machined directly in the metallic shell 217, or anadditional element of a suitable material capable of absorbing shocks,for example of rubber or elastomer.

The second mobile element 220 can, in this embodiment, take up 7 indexedpositions at a distance of 15 degrees from one another, for a totalangle of 90 degrees. This angle, when combined with the 360 degrees ofrotation possible for the first rotating element 210, allows the feeler30 to be oriented in a number of directions uniformly distributed in ahalf-space. It would however be possible to realize the inventive devicewith a generic number of indexed positions and having whatever distancebetween them.

FIGS. 4, 5 a and 5 b show a second embodiment of the invention, in whichthe disengaging mechanism 300 of the first axis 211 is achieved withfour pairs of identical and symmetrical connecting rods 320.

In this embodiment, each pair of connecting rods 320 is articulatedrelative to a central point 323 and the external forces applied to thebuttons 310 are transmitted to said central points 323 when the two endsof the two connecting rods of a pair rest one on the fixed element 250and the other on the first mobile element 210.

In this disposition, the reduction ratio between the axial force exertedon the mobile element 210 and the radial operation force applied to thebuttons 310 is proportional to the tangent of the half aperture anglebetween the connecting rods 320. There results a reduction ratio thatincreases with the distance between the elements 250 and 210 and theangle between the connecting rods 320. This variability of the reductionratio is advantageous since the force required for holding the buttonspushed at the end of their run is minimal, which makes easier theoperation of finely adjusting the feeler 30.

This advantageous characteristic is also possible in the firstembodiment by using a non-plane surface instead of the inclined plane302.

When the buttons 310 are pressed fully, the distance between the spheres226 and the pins juxtaposed thereto is maintained, and the spheres andpins cannot in any case come into contact with one another or with otherelements of the probe's mechanism. Under this condition, wear of theindexing surfaces is reduced to the required minimum, and the indexingaccuracy is kept through time.

When the user presses on two opposed buttons 310, the resulting force onthe first mobile element 210 through the connecting rods 320 issubstantially axial relative to the rotation axis 211, i.e.substantially aligned and opposed to the force exerted by the spring215, which ensures rectilinear movements without jamming. On the otherhand, if the operator pushes asymmetrically on only one of the buttons310, the horizontal component of the resulting force produces a highfriction between the rod 253 and the sleeve 219 preventing the firstmobile element 210 from being disengaged. This advantageouscharacteristic allows ill-timed and involuntary operations to beprevented.

The buttons 310 are surrounded by a protective ring membrane of rubberor elastomer 330, whose function is to protect the internal mechanismfrom dirt and dust, but also to prevent the transmission of heat fromthe user's hands to the internal indexing mechanism, which would havedire consequences on the indexing accuracy. With the same purpose, thebuttons 410 and 411, serving for the rotation and disengaging of thesecond axis 212, are also preferably made of a synthetic material havinggood heat-insulating properties.

A window 41 is provided on the supporting element 250 to allow therotation angle relative to the first axis 211 to be read on a scaleengraved or printed on the first mobile element 210, as can be seen inFIGS. 5 a and 5 b.

The rotation angle relative to the second axis 212 can be read on thetwo windows 40 provided in the external crown of the button 411 andvisible in FIGS. 5 a and 5 c. Two windows are necessary in this case toallow an optimal visibility in all the probe's possible orientations.

The trigger feeler 30 reacts to the slightest contact with the surfaceof the piece to be measured by generating an electric impulse. Theimpulse is transmitted, through an electronic processing circuit (notrepresented), to the connector 70 for connecting with the measuringmachine's control device and to the light indicator 50. The indicatorcomprises in this embodiment a light diode but could alternativelycomprise other known light emitters, such as for exampleelectro-luminescent elements in sheet or wire form. The light diode istopped with an optical light diffuser allowing the emitted light to beseen in a large range of observation angles.

In an alternative embodiment of the invention, the indicator 50 isreplaced with several indicators placed at different locations on theprobe so that at least one indicator is visible from every possibleobservation angle.

In another embodiment of the inventive device, the indicator 50comprises one or several light conductors for emitting the lightproduced by one or several light sources from different locations of theprobe's surface, so that the light indication is visible from everypossible observation angle.

The inventive device could also be achieved without using an indexingmechanism but with simple friction mechanisms allowing the axes to belocked in an infinite number of orientations.

The invention also comprises an embodiment in which the rotation and thedisengaging of the axes are performed by automatic actuators, forexample electric motors and/or solenoids.

In another embodiment of the invention, the rotation of the probe's axesis ensured by servomotors comprising encoders for measuring theorientation angles of the feeler. In this case, the indexing mechanismdescribed here above can be maintained or dispensed with if theservomotors' positioning accuracy is sufficient for the intendedapplications.

1. Adjustable touch-triggered probe for orienting a measuring feelerrelative to a measuring apparatus, comprising: a supporting element; afirst mobile element connected to said supporting element through afirst axis for turning said first mobile element relative to saidsupporting element; a first resilient device for holding said firstmobile element in a locked position, preventing said first mobileelement from rotating; a second mobile element connected to said firstmobile element through a second axis for turning said second mobileelement relative to said first mobile element; a second resilientdevice, that can be actuated independently from said first resilientdevice, for holding said second mobile element in a locked position,preventing said second mobile element from rotating; a first actuator inopposition to said first resilient device, for disengaging said firstmobile element, allowing said first mobile element to rotate around saidfirst axis, and a second actuator, independent from the first actuator,for disengaging said second mobile element, allowing said second mobileelement to rotate around said second axis.
 2. Probe according to claim1, wherein said first actuator disengages said first mobile element bythe action of two external forces essentially symmetrical and opposedbeing applied to said first actuator, and/or second actuator disengagessaid second mobile element by the action of two external forcesessentially symmetrical and opposed being applied to said secondactuator.
 3. Probe according to claim 2, wherein said first actuatordrives said first element in rotation through the action of a torque ofexternal forces applied to said first actuator and/or said secondactuator drives said second element in rotation through the action of atorque of external forces applied to said second actuator.
 4. Probeaccording to claim 2, wherein said first actuator and/or said secondactuator comprise means for ceasing the actuator's action when the twosaid external symmetrical and opposed forces are interrupted.
 5. Probeaccording to claim 2, wherein said first actuator and/or said secondactuator comprise a demultiplying mechanism for reducing the intensityof the force required for disengaging said first respectively secondmobile element.
 6. Probe according to claim 5, wherein saiddemultiplying mechanism comprises means for providing an increasingdemultiplication ratio for ultimately reducing the force required forkeeping said first respectively second mobile element in disengagedposition.
 7. Probe according to claim 5, wherein said demultiplyingmechanism comprises at least two pairs of symmetrical connecting rods,each pair being articulated relative to a central point, said externalforces being transmitted to said central points.
 8. Probe according toclaim 5, wherein said demultiplying mechanism comprises at least onehelical surface forming an inclined plane or an inclined curved surfaceand driven in rotation by at least two racks on which said externalforces are exerted.
 9. Probe according to claim 5, wherein saiddemultiplying mechanism comprises at least one lever with unequal arms.10. Probe according to claim 2, wherein said two external forces have adirection essentially perpendicular to said first axis and said twoexternal forces are supported by at least two buttons placed on saidprobe in positions diametrically opposed relative to said first axis.11. Probe according to claim 1, comprising one or several windows forindicating the angular position of said first and/or of said secondmobile element.
 12. Probe according to claim 11, comprising at least twowindows for indicating the position of said second mobile element. 13.Probe according to claim 1, wherein the disengaging of said first mobileelement is effected by displacement in the direction of said first axisand/or the disengaging of said second mobile element is effected bydisplacement in the direction of said second axis.
 14. Probe accordingto claim 1, comprising first indexing elements for defining amultiplicity of predetermined and reproducible angular positions forsaid first mobile element and/or second indexing elements for defining amultiplicity of predetermined and reproducible angular positions forsaid second mobile element.
 15. Probe according to claim 4, comprising amechanism for keeping apart said first and/or second indexing elementsduring rotation of said first and/or second mobile elements.
 16. Probeaccording to claim 1, comprising a measuring feeler fastened to saidsecond mobile element.
 17. Probe according to claim 1, comprising alarge-size light indicator allowing the probe's functioning to becontrolled in all measuring positions.
 18. Probe according to claim 17,comprising several light-emitting elements placed in various positionsfor allowing the probe's functioning to be controlled in all measuringpositions.
 19. Probe according to claim 1, comprising an externalthermically insulating layer for avoiding the conduction of heat fromthe hands into the probe.
 20. Probe according to claim 1, comprisingprotecting elements protruding from the part of the body of said probeadjacent to the feeler, for protecting the internal mechanism during anaccidental shock of said probe.
 21. Probe according to claim 1, whereinthe action of said first actuator on said first mobile element issubstantially aligned and opposed to the force exerted by said firstresilient element onto said first mobile element.
 22. Probe according toclaim 1, wherein the action of said second actuator on said secondmobile element is substantially aligned and opposed to the force exertedby said second resilient element onto said second mobile element.